1. Field of Use
This invention relates generally to an article of manufacture such as a crawler track shoe for a mining shovel or the like, having a cylindrical hole for receiving a pin which pivotally connects the shoe to an adjacent shoe.
The invention further relates to a method for providing such an article in which the wall defining the hole is work-hardened to reduce wear caused by pin movement and tension loads.
2. Description of the Prior Art
Some large heavy-duty machines such as mining shovels, tractors, cranes and the like, employ ground-engaging crawler type assemblies for support and propulsion. These assemblies include endless crawler tracks which are made up of individual crawler track shoes which are pivotally connected to one another by pivot pins which engage holes in the shoes. Such shoes, which are typically manufactured from cast or machined steel alloy castings, are subjected to severe wear and abrasion on those surfaces which contact the ground or bear against other metal components. For example, in a crawler shoe the distance between the pins which connect one shoe to another changes as the shoe and pin holes are subjected to operational forces. The pin wears the hole surface and also causes the hole or hole supporting structure to lengthen. This change in pitch from shoe to shoe creates secondary problems on the driving mechanism, normally called the tumbler. Heretofore, the shoes and pins were made of various types of wear-resistant steel alloys in an effort to overcome or reduce the aforementioned problems. Some alloys which have desirable hardness characteristics when cast are difficult and costly to machine after casting. It is known, however, that some manganese steel alloys can be hardened after casting and machining by subjecting them to the application of force from external energy sources. Thus, the normal way of hardening such alloys is through operations such as machining, through impact such as hammering or shot peening, or through impact occurring under normal operating conditions. One type of alloy identified as Hadfield Manganese Steel Alloy changes from a hardness of about 23 Rockwell C up to about 50 or 55 Rockwell C. This increased hardness not only increases wear resistance but also reduces potential dimensional changes in the finished product.